feat: add dynamic_win_width option for tags window

[awerebea]

Summary

Add a dynamic_win_width setting that automatically sizes the tags window to fit the longest tag
path rather than using a fixed width.

How it works:

• Accepts a number between 0 and 1 (exclusive) representing the maximum width as a fraction of
  the editor width, or false (default) to keep the existing static-width behavior.
• win_opts.width is repurposed as the minimum floor: the computed width is clamped between
  win_opts.width and vim.o.columns * dynamic_win_width.
• Width calculation accounts for: display style (relative strips the scope path prefix,
  basename uses only the filename), optional tag names rendered as EOL virtual text, icon
  padding, and the index/separator overhead (/001 + icon = ~10 cols with icons, ~7 without).
• open_window(content, win_opts?) gains an optional second parameter so computed opts are passed
  per-call without mutating global settings.

No breaking changes. Default is false; existing configs behave identically.

-- Example
require("grapple").setup({
    dynamic_win_width = 0.8,  -- max 80% of editor width
    win_opts = {
        width = 40,           -- minimum width (floor)
    },
})